Refactor memory allocation and method stubs in ggml-hexagon

- Improved code readability by aligning struct members and function parameters.
- Enhanced error handling in _stub_method and related functions.
- Updated memory allocation logic in _allocator_alloc to ensure proper alignment.
- Removed commented-out code and unnecessary error messages for clarity.
- Ensured consistent formatting across the file for better maintainability.

Author: l3utterfly